Ayad Ag Ghaly, leader of the faction of tribal Tuareg fighters that is allied to al-Qaeda, was reported to have carried out the sentence on an unnamed "vandal" in the heart of the ancient city.

Ousmane Halle, the mayor of Timbuktu, said almost all of the city's 300 Christians had fled after Ag Ghaly announced that Sharia law would be enforced.

He told local radio that women should be covered at all times, warned thieves they would have their hands cut off and adulterers they would be stoned.

His faction, named Ansar al-Din, and its al-Qaeda allies won control of the urban centres of northern Mali after a regional uprising in the wake of a military coup that deposed the country's elected government.

While another faction of the Tuareg rebellion, the National Movement for the Liberation of the Azawad (MNLA) announced a ceasefire yesterday in response to international appeals, the extremists consolidated their grip on key cities.

Algeria said its consulate in Gao, another town under Ansar al-Din's control, had been overrun. The consul and six staff had been taken hostage.

"The Algerian government is doing everything possible to ensure they are freed as quickly as possible," said Mourad Medelci, Algeria's foreign minister said.

While international concern has continued to focus on the restoration of democracy, fears that al-Qaeda had gained a safe haven in the nomadic north have emerged with the fall of Timbuktu, Gao and Kidal.

Diane English and Neil Whitehead, a British couple, who were evacuated from Timbuktu by MNLA fighters, were yesterday resting at the home of the British envoy in neighbouring Mauritanian. They planned to travel back to the UK as soon as possible.

"We can confirm that they have arrived safely in Mauritania, where they have been offered consular assistance," a Foreign Office spokesman said.

French President Nicolas Sarkozy demanded the military junta that overthrew Mali's president Amadou Toumari Toure restore power to civilian leaders as a first step to bringing order to the country.

"President Toure was a democrat, who had decided not to present himself in the next elections," Mr Sarkozy said. "So there was no reason to interrupt the electoral process. It's a scandal."

West African leaders were attempting yesterday to forge a deal to send regional forces to the country to enforce a ceasefire.

Some hope emerged from a meeting between Djibrill Bassole, Burkina Faso's Foreign Minister and the coup leader Capt Amadou Sanogo.

"We will do everything we can so that these sanctions are not only suspended, but completely lifted and abandoned. We are on the road," he said. "I can assure you that the captain has the right attitude and will soon have an announcement to make that goes in the right direction. I prefer leaving it up to him to announce it."

Alain Juppe, the French foreign minister, said that Paris would provide support for a 3,000-strong West African intervention force. He estimate that Tuareq rebels and fighters from al-Qeada in the Islamic Maghreb (AQIM) numbered more than 1,000. He said: "We have judged the number of fighters, Tuaregs and AQIM together, at around a small thousand."